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CHAPTER 5 Generation and Conduction of Action Potentials be conducted very rapidly from one node of Ranvier to the next. This makes the action potential appear to jump from node to node in a form of conduction called saltatory conduction.
9.
A receptor responds preferentially to a particular form of stimulus energy. Its receptive field is that part of a sensory domain in which energy can affect the receptor.
10.
Receptor potentials are the result of transduction of sensory stimuli. These potentials reflect the specific parameters of the stimulus and, if they exceed threshold, alter the action potential firing patterns of the afferent neurons.
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Sakmann B, Neher E. Single-Channel Recording. 2nd ed. Philadelphia: Springer; 1995.
Upon completion of this chapter the student should be able to answer the following questions: 1.
What are the characteristics of electrical synapses?
2.
What are the specializations found in the presynaptic and postsynaptic elements of a chemical synapse?
3.
What sequence of events connect the arrival of the action potential at the presynaptic terminal to the entry of calcium?
4.
What sequence of events connect the entry of calcium at the presynaptic terminal to release of neurotransmitter?
5.
What is the quantal hypothesis of synaptic transmission, and how does the presence of miniature end plate potentials support this hypothesis?
6.
Why is the reversal potential of a typical EPSP near 0 mV?
7.
What distinguishes EPSPs and IPSPs in terms of underlying ionic conductances, effect on membrane potential, and neuronal firing probability?
8.
How does an IPSP still inhibit a neuron when its reversal potential is equal to or more positive than the neuron’s resting potential?
9.
What are the mechanisms by which synaptic effects can change over time?
10.
What are the criteria for determining a substance is a neurotransmitter, and what are the major excitatory and inhibitory neurotransmitters?
11.
What are the major classes of neurotransmitter receptors?
ynaptic transmission is the major process by which electrical signals are transferred between cells within the nervous system (or between neurons and muscle cells or sensory receptors). Within the nervous system, synaptic transmission is usually conceived of as an interaction between two neurons that occurs in a point-to-point manner at specialized junctions called synapses. Two main classes of synapses are distinguished: electrical and chemical. However, as the list of chemical neurotransmitters has grown and as understanding of their mechanisms of action has increased, the definition and conception of what constitutes synaptic transmission has had to be refined and expanded. We no longer think of synaptic transmission as a process that involves only neurons, but now realize that glia form an important element of the synapse and that signaling occurs between neurons and glia. Moreover, in some cases, neurotransmitter released at a synapse will act over a widespread territory rather than just at the synapse from which it is released. Thus, we must either generalize the definition of synaptic transmission or consider classically defined synaptic transmission as but one of several mechanisms by which cells in the nervous system communicate with each other. In this chapter we first describe the classic conception of synaptic transmission (electrical and chemical) and then introduce some of the nontraditional neurotransmitters and discuss how they have forced modifications in our conception of chemical communication between cells in the nervous system.